Climate models suggest the overturning circulation in both the Northern and Southern hemispheres is sensitive to climate change (e.g.,1). Enhanced greenhouse warming is expected to drive a more vigorous hydrological cycle, with increased precipitation at high latitudes and increased evaporation at low latitudes. The resulting reduction in surface salinity reduces the formation of dense water at high northern and southern latitudes. Palaeoclimate records demostrate that changes in the overturning circulation have been associated with large and abrupt climate changes in the past (e.g., 2). Southern Ocean overturning is thought to exert a strong control on global productivity and CO23, and changes in strength of the Southern Ocean overturning circulation have been linked to changes in the ocean uptake and release of carbon dioxide, both in the present-day ocean and in association with glacial-interglacial cycles.
For more detailed information on the science rationale behind Theme 2 please download the SOOS Initial Science and Implementation Strategy.
Sustained observations of temperature, salinity, stratification and ventilation are needed to detect changes in the overturning in response to changes in atmospheric forcing. The observations need to span the entire water column, and need to include carbon, oxygen and other tracers.
Monitoring of Mertz Polyna. Photo: S. Rintoul CSIRO